A conventional type of plate heat exchanger use heat transfer plates fitted with gaskets that seal off each channel from the next, and direct the fluids into alternate channels. This type of plate heat exchanger is used throughout industry as standard equipment for efficient heating, cooling, heat recovery, condensation and evaporation.
Such a plate heat exchanger consists of a series of thin corrugated heat exchanger plates fitted with gaskets. The plates are then compressed together between a frame plate and a pressure plate in order to create an arrangement of parallel flow channels. The two fluids flow in alternate channels which gives a large surface area over which the transfer of heat energy from one fluid to the other can take place. The channels are provided with different corrugated patterns designed to induce maximum turbulence in both the fluid flows in order to make heat transfer as efficient as possible. The two different fluids normally enter and leave at the top and bottom of the heat exchanger, respectively. This is known as the counter-current flow principle.
One advantage with heat exchangers having gaskets compared with brazed heat exchangers is that it is easy to separate the heat exchanger plates. This is of advantage e.g. when they need to be cleaned or when the capacity of the heat exchanger is to be adjusted. This is done by simply adding or removing heat exchanger plates when required.
In one type of plate heat exchangers, the heat exchanger comprises one type of plate, which is mounted with every other plate rotated 180 degrees to form two different channels for the fluids, one channel for the cooling medium and one channel for the product that is to be cooled. A sealing is provided between each plate. Such an arrangement is cost-effective and works for many applications. Each plate is provided with ridges and valleys in order to on one hand provide a mechanical stiffness and on the other hand to improve the heat transfer to the liquid. The plates will bear on each other where the patterns of the plates meet each other, which will improve the mechanical stiffness of the plate package. This is important especially when the fluids have different pressures. For this type of heat exchanger, the inlet and outlet opening regions must be adapted so that they work for both channels.
In a heat exchanger channel, it is of advantage that the temperature distribution over the channel width is as even as possible. An uneven temperature distribution will influence the efficiency of the heat exchanger in a negative way. This is e.g. the case for a fluid that is to be heated. With an uneven temperature distribution, part of the fluid will be heated more than enough while part of the fluid is heated less than enough. At the outlet port, the fluid is mixed which means that part of the heated fluid will be cooled by the other part of the fluid.
The problem with an uneven temperature distribution is present in most heat exchangers. This is due to the fact that the inlet and outlet ports are arranged in a non-symmetric way with regards to the heat transfer surface of the heat exchanger. In a conventional heat exchanger, the inlet and outlet ports are arranged at the corners of the heat exchanger plates. In this way, the heat transfer surface is held as large as possible. The disadvantage of this arrangement is that the distance that the fluid must travel differs over the plate width.
Different approaches to solve this problem are known. It is common to improve the flow distribution by using different types of patterns in the flow channel. In larger heat exchangers, a specific pattern is used in the distribution area of the heat exchanger, and another pattern is used in the heat transfer area of the heat exchanger. The purpose of the different patterns is to increase the pressure drop over the heat transfer channel in order to distribute the fluid more even. It is however not possible to increase the pressure drop too much. For smaller heat exchangers, it is not possible to have a specific distribution area due to the size of the heat exchanger plates. In heat exchangers comprising different heat exchanger plates, it is possible to have different distribution patterns for the different flow channels. This is not the case for heat exchangers comprising only one type of heat exchanger plates.
In application JP 09152127, a heat exchanger having heat exchanger plates with flat areas is shown. Each heat exchanger plate is provided with three areas with a chevron shaped pattern and there between two flat areas with no pattern at all. The purpose of this design is to allow the water flow to mix in the flat areas, thereby equalising the temperature distribution in the heat exchanger. This solution may work for larger heat exchangers, where size is not an issue, but seems to be rather space consuming. The flat surfaces will reduce the effective heat transfer surface, which makes the heat exchanger rather large. The pattern is also asymmetric lengthwise which requires a two-plate design of the heat exchanger.
These solutions may function for some applications, but they still show some disadvantages. There is thus room for improvements.